Eyewear used for sports is typically designed to wrap around the user's face and sufficiently seal against the skin to create a dead air space between the glasses and the user's face (hereinafter referred to as the "dead space"). As the user engages in strenuous activity, the heat and moisture can build up in the dead space, making the glasses uncomfortable to wear and producing condensation on the inside surface of the lenses which can partially or entirely obstruct the vision of the wearer. This phenomenon is commonly known as "fogging."
There have been many prior art methods attempted to reduce or eliminate fogging. Some devices, such as that described in U.S. Pat. No. 4,707,863, describe chemical coatings which can be applied to the inside surface of a lens to alleviate fogging. Such coatings, however, tend to enhance fingerprints caused by handling, and are typically not durable, tending to wear off when the user cleans the lenses.
Therefore, different types of ventilation have been relied upon to alleviate fogging. Many prior art sunglasses and protective glasses or goggles provide openings in the frame above and below the lenses to allow air to flow in and out. These are not believed to be particularly effective at preventing fogging when a wearer is engaged in particularly strenuous activity, since there is nothing to cause the air to actually flow through the dead space, unless the wearer tilts his head downward towards the ground as he is moving forward to allow the passing air to flow through the perforations in the frame. This is not particularly desirable when the wearer is moving forward at great speed (for example, when riding a motorcycle) because such action will take the wearer's eyes off the space in front of his vehicle and may result in an unfortunate accident. Moreover, when the user can generate a flow through the dead space, there is no way to control the amount of air throughput or turn it off when it is no longer desired. Finally, open apertures will typically allow the ingress of dust and particulate matter into the dead space where it can be blown into the unprotected eyes by the flow of air, which is also very undesirable.
U.S. Pat. Nos. 5,191,364 and 5,428,411 substantially reduced or eliminated the ingress of dust and particulate matter into the dead space by covering the ventilation apertures with permeable foam, and further addressed the fogging problem with coated and/or double lenses. However, these glasses still suffer from the lack of a motivating force for causing a flow of air through the ventilating apertures without causing the wearer to take his eyes off his direction of travel.
British Patent Specification 364,970 addressed the problem of controlling a flow of air through the dead space by providing a valve which may be adjusted by loosening a screw, rotating an inlet regulating disc to a desired position, and then tightening the screw. This device is not desirable because the user must remove the glasses, produce a screw driver, loosen the screw, rotate the disc, tighten the screw, put the glasses back on and use them at the desired speed to determine if the disc has been rotated to a position which will produce the desired flow under the specific conditions of use. If not, the procedure must be repeated over and over again until the desired flow is obtained.
Accordingly, the need exists for sunglasses and protective glasses which automatically generate a flow of filtered air through the dead space which can be easily adjusted by the user while wearing and using the sunglasses, without the need for removing them.